Early-Age Heat and Temperature Profiles in Concretes Made With High g
Proportions of GGBS and Fly Ash in the Cement BindersCement Binders
Yunus BallimYunus BallimSchool of Civil and Environmental Engineering
University of the WitwatersrandJohannesburg, South Africa
Overview
• Measuring the rate of heat evolution from cement• Form of expression of the heat rate functionp• Effect of cement extenders on measured heat rate• Brief description of the Wits University p y
temperature prediction model• Effect of cement extenders on temperature p
development in a large concrete element
WITS Adiabatic CalorimeterUPS
A/D Convertor
SignalConditioning
MotorInterface circuits
and relaysPolystyrene cover
Tank
Motor
Stirer Tank heater
Tank temperatureprobe
Personal Computer
Water
Personal Computer
SampleChamber
Sample Sample Temperatureprobe
40
)
25
30
35 pe
ratu
re (d
eg. C
)
15
20
Tem
p
0 10 20 30 40 50 Time (hours)
2 5
3
3.5
bind
er)
150
200
f bin
der)
Total Heat
0 5
1
1.5
2
2.5
at R
ate
(W/k
g of
50
100
al H
eat (
kJ/k
g of
Heat Rateq C T Tm
t p t os .( )
0
0.5 H
ea0 To
ta
0 10 20 30 40 50 Time (hours)
Heat Rateq Cmt p t o
c.( )
Normalise the heat rate curve toheat rate curve to
q
as a function of MaturityM
as a function of Maturityand convert to clock time by
dtdM
Mq
tq
dtMt
Arhenius MaturityNormalisation
6
W/k
g)
Start Temp (oC)
0
2
4
Hea
t Rat
e (W 13
2129
Start Temp (oC)Mix ACEM I
00 20 40 60 80 100
Time (hrs)
2
3
heat
rate
1321
Start Temp (oC)
Mix A
0
1
0 50 100 150 200 250 300
Mat
urity
h 2129(CEM I)
0 50 100 150 200 250 300
Arrhenius Maturity (t20 hours)
2 0
2.5
3.0e
(W/k
g) 100% CEM 120% GGBS
1.0
1.5
2.0
rity
Hea
t Rat
e
40% GGBS60% GGBS80% GGBS Material Mass (g)
Binder St
420 1020
0.0
0.5
0 20 40 60 80 100
A h i M i ( h )
Mat
u StoneSand Water
10201060 280
Arrhenius Maturity (t20 hours)
2 5
3.0
kg) 100% CEM 1
1.5
2.0
2.5
eat R
ate
(W/k
20% FA40% FA60% FA80% FA
Effect of cement
0.5
1.0
Mat
urity
He 80% FAcement
extenders0.0
0 20 40 60 80 100
Arrhenius Maturity (t20 hours)
Effect on peak heat rate
4.0
W/k
g) A2640 A3206 A3880
A4400 A4980
2.0
3.0
rity
Heat
Rat
e (W A4400 A4980
Clinker A cements
0.0
1.0
0 10 20 30 40 50 60
Mat
ur
Maturity (t20 hours)
4 0
3.0
4.0
at R
ate
(W/k
g)
B2660 B3190 B3860
B4384 B4943
Clinker B cementsEffect of cement
1.0
2.0
Mat
urity
Hea
B4384 B4943
fineness
0.00 10 20 30 40 50 60
Maturity (t20 hours)
Modeling temperature development in mass concrete:development in mass concrete:
The WITS University temperature prediction model
TEMPERATURE PREDICTION MODEL
Element Modeled
T A
Element Modeled
Air
Tem
p. T
Concrete Block
Rock: k = kR; Temp = TR = f(τ)Time, τ
Finite Difference Analysis NodesN N
Finite Difference Analysis Nodes
PW E
S
PW E
R = node in rock
Δ; kR
S
(a) P is an internal node (b) P is a bottom node on rock
h TAPW
NP
ETA
h
PW
S
S
(d) P is an exposedsurface node(c) P is a corner node
Ambient Temperature ModelAmbient Temperature ModelT
T T T TA
d m
sin
( ) max min max min2 TA sin .
24 2 2
25
15
20
e (d
eg. C
)
5
10
Tem
pera
ture
0
5
Air
0 50 100 150 200 250
Measured Model
Time after casting (hrs)
Concrete profile modeledConcrete profile modeled• k=2,7 W/m.K (Granite aggregate)• Cp=1150 J/kg.K• h=25 W/m2.K for exposed surfacesp• h=5 W/m2.K for surfaces with formwork
(timber for the first 18 hours)(timber for the first 18 hours)• Concrete cast at 10h00 at To=15 oC;
A bi t t b t 12 oC d 25 oC• Ambient temp between 12 oC and 25 oC.• Finite difference x = y = 250 mm
Concrete element
• Concrete = 5m wide x 2m high• Concrete mixture details:Concrete mixture details:
Cem D 40% FA 60% FA 40% GGBS 60% GGBS Cem D 40% FA 60% FA 40% GGBS 60% GGBSBinder Water Sand
200 160 600
215 160 500
230 160 500
215 160 585
230 160 570
Stone 1600 1680 1660 1600 1600
GGBS Concretes
40
GGBS Concretes
303540
e (o
C)
100% CEM I
40% GGBS
202530
erat
ure
101520
Tem
pe 60% GGBS
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Distance from side face (m)Distance from side face (m)
Fly ash concretes
Fly ash concretes
303540
e (o
C)
100% CEM I
202530
erat
ure
40% FA
101520
Tem
pe 60% FA
10
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Di t f id f ( )
T
Distance from side face (m)
General Characteristics ofGeneral Characteristics of Temperature Development
Cem D 40% FA 60% FA 40% GGBS 60% GGBS Cem D 40% FA 60% FA 40% GGBS 60% GGBSTMax (oC)
tMax (t20 hrs) ΔTMax (oC)
35 80 20
25 72 11
22 64 8
28 94 13
27 116 13Max ( )
tΔT(t20 hrs) 90 66 64 90 114
Caution: Late temperatureCaution: Late temperature development
Future Work
• Develop a physico-chemical model for the maturity-based heat rate functiony
• Incorporate extenders at a fundamental level• Improved understanding and definition of• Improved understanding and definition of
boundary conditions in the modelAll f diff l fi i• Allow for different structural configurations
• Develop a cracking model
THANK YOU
With much acknowledgement to:• My research assistant Dr Peter GrahamMy research assistant, Dr Peter Graham• The Cement & Concrete Institute, Eskom
and the National Research Foundation (SA)and the National Research Foundation (SA) for generous funding support